fix(agent-skill): use executable fleet rollout route

[andrei-hasna]

Summary:

• Add fleet-package-rollout to the canonical repository-managed agent skill corpus.
• Replace the non-executing machines ssh instruction with reviewed manifest-backed machines apps plan/apply execution.
• Add literal positive and negative controls plus a regression that forbids private-target and raw SSH fallback.

Validation:

• bun run typecheck: rc 0
• bun run build: rc 0
• bun run test: 1078 pass, 0 fail
• bun run verify:release: passed
• bun test src/lib/agent-workflow-skills.test.ts: 7 pass, 0 fail
• open-machines bun test test/apps.test.ts: 7 pass, 0 fail, including selected-machine execution
• installed machines 0.2.15 negative control: rc 1 with private-target refusal and no rollout output
• gitleaks staged and origin/main..HEAD scans: no leaks found

Review:

• Adversarial self-review used because task instructions prohibited subagents. One reachable rollback ambiguity was fixed and focused revalidation passed.

Task: ca7fb4e7-466a-441d-89e8-39928370f116

Rollout boundary:

• No installed skill copy, skill-sync distribution, package publish, merge, or fleet-wide rerender was performed.

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